Cyrix-ct 12/24-120
Victron Cyrix-ct 12/24V 120A wiring diagram
Cyrix-ct 12/24-120 voltage-sensing combiner for common-negative battery banks: 120 A continuous, 180 A for 5 seconds. Requires a separate negative control connection; optional start assist. No charge-current regulation or lithium BMS control.
Wiring diagram
How the Cyrix-ct 120 is wired.
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Cable sizing for this example
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Installation notes
Before you install.
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Verified against the manufacturer's documentation (rev. Rev 05 — 08-06-2022), checked 2026-10-01. Manufacturer documentation →
Which Cyrix does this entry represent?
This is the Cyrix-ct 12/24-120, a voltage-sensing battery combiner for a common-negative system. It is distinct from the Cyrix-Li models with lithium-BMS control. The installation manual, PDF page 1, also discusses a 24/48 V variant; that does not extend this catalog model's voltage range to 48 V.
It parallels the banks directly when charging is detected. It does not limit alternator current, select a charging profile, or isolate incompatible battery chemistries.
How do A and B map to the real connections?
The catalog's A/B represent the two brass battery-positive studs, numbered 87 and 30 on the hardware. The manual diagram places the starter side on 87 and domestic-bank side on 30. The small 86 / battery minus connection supplies the electronics' common-negative reference.
Optional 85 / start assist receives battery positive through a switch; the manufacturer's diagram shows a 0.1 A fuse in this command lead. A momentary command holds the relay closed for 30 seconds. A maintained switch holds it closed while operated. Neither control wire is a high-current battery connection.
How should protection and capacity be chosen?
The manual specifies 120 A continuous and 180 A for five seconds for cranking. Size the series fuse for the actual cable and circuit, with a fuse rating no greater than 120 A. The drawing's main fuse value is a limit, not evidence that every cable can support it. Review protection wherever either battery can feed a damaged conductor.
The 120/230 A datasheet identifies the 120 A unit's main hardware as M6. No model-specific tightening torque was established in these downloaded documents; obtain it for the supplied hardware rather than using an M8 sibling's value.
What should commissioning establish?
The relay senses both banks, so charging the domestic bank can also connect the starter bank. Its voltage-trend logic uses variable delays; it need not close immediately when voltage rises. Thermal protection opens an overheated relay and reconnects after cooling.
This 120 A model has no status LED. Check battery voltages, the common-negative lead and actual relay operation after wiring. The catalog omits terminal 86, start-assist wiring, its small fuse and the bank configuration. An A/B-only drawing is therefore an incomplete installation, even when the two main cables are correctly sized.
Fit check
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Technical reference
Specifications and terminal map.
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Catalog specification
Cyrix-ct 12/24-120 voltage-sensing combiner for common-negative battery banks: 120 A continuous, 180 A for 5 seconds. Requires a separate negative control connection; optional start assist. No charge-current regulation or lithium BMS control.
Connection limits are listed in the terminal map. Use the manufacturer's documentation for the full specifications.
Terminal map
Catalog connection points, current direction and planning limits. Check the manufacturer's pinout and connector ratings before installation.
A
neutral · input
B
neutral · output
Sources and sizing method
Equipment specifications. Model details, ratings and terminal roles come from the catalog. Check your unit’s label and current manufacturer documentation for its exact revision.
Example sizing. Wire sizes and fuse ratings apply to the connected example, not a fixed cable size for this component. Set your actual equipment, current, lengths and installation conditions in Crimp before choosing hardware.
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